1. Field of the Invention
The present invention relates to a toner for developing a latent electrostatic image, which does not cause toner spillage from a developing unit and formation of streaks on a toner bearing member (hereinafter, referred to as “toner conveying member” and “developing roller”) due to operation of an image-forming apparatus for a long period of time, and does not impair image quality, and the present invention also relates an image-forming method, an image-forming apparatus and a process cartridge using the toner.
2. Description of the Related Art
Currently, there is a trend that a full-color print replaces a monochrome print in copiers, printers and Multifunction Peripherals (MFP) using an electrophotographic method.
Above all, the printers and MFPs which are used in Small Office Home Office (SOHO) or placed dispersively in an office are shipped in large volume. For these applications low price and compact ones are desired. The printers and MFPs employing a nonmagnetic one-component developing process are advantageous to meet such needs because they are constructed from small number of components, and do not need a space for mixing with magnetic particles.
The nonmagnetic one-component developing process is performed by the following steps: applying charge to a toner by friction by means of a toner layer thickness control member contacting with a toner bearing member (developing roller) (frictional charge), simultaneously coating the toner bearing member thinly with the toner, and then conveying the toner to a developing area in which the toner bearing member and a image bearing member face each other, and developing a latent electrostatic image on the image bearing member to be visible as a toner image.
However, in the nonmagnetic one-component developing process, the following phenomena may occur: a phenomenon of toner spilling from between the toner layer thickness control member and the toner bearing member in a developing unit, which is termed as “toner spillage”; and a phenomenon of the toner lacking streaky in a circumferential direction on the toner bearing member, which is termed as “streaks on the toner bearing member”. When toner spillage occurs, the inside of the device such as a printer, a MFP and the like are smeared by the toner. This may cause not only smear on print, and on hands or clothes of a user when the user replaces consumable supplies such as a toner bottle, toner cartridge, and process cartridge, but also device failure due to contact failure of an electrode contact point and torque up of a moving portion. Moreover, when streaks occur on the toner bearing member, a streaky image failure is generated on a print, and print quality is significantly impaired.
The toner spillage can be reduced to some extend by strengthening the contact pressure between the toner layer thickness control member and the toner bearing member. However, a part of the toner component is fused in the contact part between the toner layer thickness control member and the toner bearing member due to excessive contact pressure, and the toner cannot be coated uniformly on the toner bearing member. Thus the toner is frictionally charged unevenly, and the poorly charged toner adheres around the non-image portion of a print (toner fog).
To solve the above problem, it has been reported that the mixing of magnesium silicates such as forsterite, enstatite, steatite and the like in a toner base allows to improve the effect (For example, Japanese Patent Application Laid-Open (JP-A) No. 05-165257, Japanese Patent (JP-B) Nos. 2933724 and 3007693). The magnesium silicate herein is MgO—SiO2 oxide (see Japanese Patent Application Laid-Open (JP-A) No. 2003-327470).
Even though the image-forming apparatus using the toner base in which the magnesium silicate is mixed in the above proposals, problems of the toner spillage from a developing unit and streaks on the toner bearing member occur when it is operated for a long period of time.